Intravenous drug use (IDU) enables the HIV epidemic in Russia; over 90% of all HIV infections occur in communities of IDUs Russia and other countries where IDLJ is a major HIV transmission route need to identify low-cost, sustainable methods of HIV prevention. In St. Petersburg, HIV prevalence in IDUs (-100,000) leapt from 4% in 1999, to 12% in 2000 and approximately 50% in early 2002. Using the research infrastructure provided by our NIAID/Fogarty-funded HIV Prevention Trials Network Unit in St. Petersburg, we will determine the efficacy of a network-orientated peer-educator intervention to prevent HIV transmission among IDUs and members of their HIV risk network. We hypothesize that a network-orientated, peer-education intervention will lead to changes in network norms that favor condom use and needle hygiene resulting in reductions in HIV incidence. Our study is a Phase III, two-arm, randomized controlled trial involving HIV (-) active IDU Index Participants (IP) and network members (NM) (individuals identified by each IP as members of their sex and/or IDU networks). There will be an average of approximately 3NM/IP. IP will be randomized in a 1:1 ratio with their NM to one of the two study arms shown below: Behavioral Intervention 1. Experimental Arm: n~330 networks (330 IP+~990 NM). Index Participants (IP) = Enhanced HIV VCT + ten 2-hour network oriented peer-educator sessions during weeks 1 to 4 + booster sessions at 6 and 12 months. Network Members (NM) = Enhanced HIV VCT 2. Control Arm: n approximately 330 networks (330 IP+ approximately 990 NM). Index Participants (IP) = Enhanced HIV VCT. Network Members (NM) = Enhanced HIV VCT. Study duration = 60 months (minimum f/u = 23 months; max f/u= 30 months). Sample size provides 90% power to detect a 40% reduction in HIV infection (6 to 3.6%/yr), loss to follow rate approximately 10%/yr; 2-sided e. =0.05. The proposed international research team -- experienced in field research in Russia and in conducting HIV prevention/behavior change interventions -- is well posed to conduct a study that will inform government policy and support for HIV prevention and drug abuse treatment efforts in Russia and other countries with rapidly expanding IDU-driven HIV burdens.